Digital projectors, such as digital micro-mirror device (DMD) and liquid crystal device (LCD) projectors, project high quality images onto a viewing surface. Both DMD and LCD projectors utilize high intensity lamps and reflectors to generate the light needed for projection. Light generated by the lamp is concentrated as a “fireball” that is located at a focal point of a reflector. Light produced by the fireball is frequently directed from the lamp to an illumination optics assembly. The illumination optics assembly then focuses the light onto a spatial light modulator that produces images and utilizes the generated light to project the image onto a viewing surface. The efficiency of the lamp depends, at least in part, on the alignment of the lamp to the illumination optics, the lamp being held in place by a lamp bracket. This is of primary concern when using elliptical reflectors.
As a result, efforts have been directed at ensuring that the illumination optics assembly is properly oriented and aligned with respect to the lamp bracket. One prior solution consisted of registration pins and mating holes on small area flats. These have multiple tolerances corresponding to the position and diameters of each set of holes. Accordingly, the location of these datums are such that positional accuracy and joint stability are not optimized. The accuracy of such a lamp bracket and illumination optics assembly is determined, at least in part, by independently formed features that are then assembled.
Each part may be formed with a certain degree of accuracy. The accuracy with which the part can be formed is known as a tolerance. For example, if a part can accurately be formed within +/−0.001 inches of the idealized part shape, it has a tolerance of 0.001 inches. If four such parts are assembled, then the corresponding accuracy of the part is additive, such that the tolerance of the assembly is no more accurate than 0.004 inches in addition to the tolerance associated with putting the assembly together.
As a result, the accuracy of the lamp receiver discussed above depends on the accuracy of each of the independently formed parts and the accuracy of the assembly. The total of these tolerances may become sufficiently large causing the image uniformity and brightness to suffer. In addition, the formation of such lamp receivers can be time consuming and hence relatively expensive.